Notch encodes a transmembrane receptor which mediates the differentiation of the nervous system as well as a very broad spectrum of other regulative decisions during Drosophila development. The developmental action of Notch is general in that it does not appear to mediate specific developmental signals but it rather modulates the ability of precursor cells to respond to such signals. In the past few years it has become clear that the mechanisms of Notch signaling are far more diverse than previously thought. This proposal addresses these new mechanisms. We aim at the identification of novel downstream effectors which are implied by the genetic analysis and the examination of the documented crosstalk between the Notch and the Ras signaling pathways. Moreover, we propose experiments which will elucidate the functional role of two newly discovered properties of the Notch molecule, its proteolytic cleavage and its apical localization in some, but not all, tissues.